Among the components of each individual vertebra of the spinal column are a vertebral body, a vertebral arch, a spinal process, two transverse processes, and two superior and two inferior articular processes. The vertebrae are connected with each other by intervertebral discs (disci intervertebralis) which contact their vertebral bodies (corpus vertebrae). These intervertebral discs, which consist of fibro-cartilage that is rich in fluid, connect the individual vertebrae with each other. The size of the intervertebral discs increases from the top of the spine to the bottom, in accordance with the stresses occurring m the human body. The intervertebral discs serve as elastic shock absorbers and provide cushions against impact. It is known that the intervertebral discs can be displaced, or that the inner gelatinous core (nucleus pulposus) may prolapse through cracks in the connective tissue-like cartilaginous outer ring (annulus fibrosus). The intervertebral disc may partly enter the intervertebral foramina (foramina intervertebralis) or the spinal canal. This prolapse can also be medial, dorsally medial or lateraL Such types of prolapse occur mostly at vertebrae L.sub.4 -L.sub.5, L.sub.6 -.sub.s 1 and C.sub.6 -C.sub.7. If such types of prolapse are not treated, they result in irreversible compression of the nerve roots or in transverse lesions. If symptomatic physiotherapy, such as exercises or message, promise no success, the discus intervertebralis must be surgically removed. Now there is a possibility of implanting an artificial intervertebral disc or performing osteosynthesis of the two vertebrae via a rigid intervertebral implant.
From EP 392 076 A1, an artificial intervertebral disc is known which consists of a superior and an inferior contact face (called upper and lower flat rigid plates in the European patent) and an elastic intermediate layer (called flat elastomeric core in the European patent). Protruding from the contact face are anchor bolts (called protuberances in the European patent) by which the intervertebral disc is fixed to the vertebral bodies. It has proven a disadvantage that due to the elastic intermediate layer between the two contact faces no optimal synthesis of the two vertebrae can be achieved.
From U.S. Pat. No. 5,192,327, a rigid intervertebral implant is known which is also inserted between two vertebral bodies for osteosynthesis. In this implant, the two vertebrae must be placed at a predetermined distance from each other before the implant can be inserted. If the distance between the two vertebrae is too great, the implant can easily slip, or it may not have a firm hold.
Both of these intervertebral implants have the disadvantage that the operation for inserting these implants must be ventral. This is not only time-consuming and costly, but also very stressful for the patient, since there is certainly a possibility that the spinal column is stabilized on the posterior side while a ventral intervention is still necessary to insert the intervertebral implant.